In recent years, the wiring lines of circuits have become increasingly fine and the number of layers of multilayer interconnection has increased due to the high integration and densification of semiconductor devices. In order to realize multilayer interconnection while attempting to miniaturize circuits, surfaces of semiconductor devices have to be planarization-processed with high accuracy.
Chemical-mechanical polishing (CMP) is known as a technique to planarize a surface of a semiconductor device. A polishing apparatus used to perform CMP is provided with a polishing table to which a polishing pad is attached, and a top ring for holding a polishing object (for example, a substrate, such as a semiconductor wafer, or various films formed on a surface of the substrate). The polishing apparatus polishes the polishing object by pressing the polishing object held on the top ring against the polishing pad while rotating the polishing table.
The polishing apparatus is provided with a film thickness measuring apparatus to detect the endpoint of a polishing process on the basis of the film thickness of the polishing object. The film thickness measuring apparatus is provided with a film thickness sensor for detecting the film thickness of the polishing object. Examples of the film thickness sensor typically include an eddy-current sensor and an optical sensor.
The eddy-current sensor or the optical sensor is disposed in a hole formed in the polishing table and detects a film thickness at the time phase of facing the polishing object, while revolving along with the rotation of the polishing table. The eddy-current sensor induces an eddy current in the polishing object, such as a conductive film, and detects the thickness of the polishing object from a change in a magnetic field caused by the eddy current induced in the polishing object. On the other hand, the optical sensor radiates light to the polishing object and measures an interference wave reflected from the polishing object, thereby detecting the thickness of the polishing object.
Incidentally, the film thickness sensor detects a film thickness while relatively moving along a surface to be polished of the polishing object along with the rotation of the polishing table. On the other hand, a magnetic field or light that the film thickness sensor uses to detect a film thickness has a spot diameter. Accordingly, in order for the output of the film thickness sensor to reach approximately 100%, the entire range of the spot diameter has to face the polishing object. That is, the entire range of the spot diameter of the film thickness sensor faces the polishing object under the condition of the film thickness sensor facing the central part of the surface to be polished of the polishing object, and therefore, the output of the film thickness sensor is approximately 100%. On the other hand, only part of the spot diameter of the film thickness sensor faces the polishing object under the condition of the film thickness sensor facing an edge part of the polishing object, and therefore, the output of the film thickness sensor does not reach 100%.
The related art is known to perform so-called edge cut processing in which processing is performed by discarding the output of the film thickness sensor in locations where the output of the film thickness sensor does not reach approximately 100% (Japanese Patent Laid-Open Nos. 2005-11977 and 2005-121616).
In the related art, however, no consideration is given to the improvement of the accuracy of detecting a film thickness.
That is, the related art performs so-called edge cut processing in which processing is performed by discarding the output of the film thickness sensor in locations where the output of the film thickness sensor does not reach approximately 100%. It is therefore difficult to detect a film thickness with high accuracy at edge parts of the polishing object.
Hence, it is an object of the present invention to improve the accuracy of detecting the film thickness of an edge part and widen the effective range of sensor output to improve the in-plane uniformity of a polishing object.